| Summary: | 碩士 === 國立臺灣大學 === 漁業科學研究所 === 98 === Japanese eel, Anguilla japonica, cannot complete its reproductive maturation in freshwater. After seawater acclimation and exogenous gonadotropins induction, the gonad of Japanese eel can mature and produce gametes. Although artificial induction can stimulate eel spermiation, spawning and success in production of glass eels, even to mature eels, the success rate of producing glass eel and survival rate of larvae are still very low. The onset of fish puberty is controlled by genetic, metabolism and environment factors. The reproductive development of eel is considered to be correlated with metabolism. The puberty onset of eel is accompanied by a silvering process. Not only reproductive maturation but the silvering are consuming processes, thus mitochondria may play an important role. So, in this study, we will examine the mitochondrial distribution and content during puberty and oogenesis, and study the reproductive development mechanism.
The cultured Japanese eels with body weight (male: 462 ± 79 g ; female: 580 ± 106 g). Depending on the color of pectoral fin, body color and external morphology, it can be distinguished into four silvering stages (Y1、Y2、S1 and S2). In fresh water, the silvering stage is mainly on Y2 stage. After artificial induction, S1 and S2 stage were shown. And there were no difference between male and female eels. Furthermore, parts of the eels possessed the features of Y2 and S1, pectoral fins became darkness, the edge of pectoral fins was colorless and ventral skin became gray and black. Moreover, after seawater acclimation the eels of particular slivering stage were increased.
In this study, the mitochondria of defolliclular oocyte were labeled with mitochondrial-specific fluorescent dye MitoTracker. There were various mitochondrial distribution patterns at different oocyte developmental stage. In the initial stage of previtellogenic oocyte, mitochondria assemble as a mitochondrial cloud (MC). There were one or two MC aggregate(s) in the oocyte during this stage. In the vitellogenic oocyte, the number of mitochondria increased significantly, dispersed in whole ooplasm and mitochondria formed small aggregates. Furthermore, the number of mitochondria increased in ovary after artificial induction with salmon pituitary homogenate and methyl testosterone. These results indicated that mitochondrial distribution patterns vary at different stages and mitochondrial population increases significantly during puberty in Japanese eel. Artificial induction also significantly increased mitochondrial population. Therefore, mitochondria may play an important role during puberty in Japanese eel, and their function during oocyte maturation needs further investigation.
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